Although smart polymer micelles able to respond to the tumor acid microenvironment are potential anticancer drug carriers, fruitful clinical application of these carriers is inadequate. For the purpose of finding the origin of the unsatisfactory therapeutic efficacy of pH-sensitive drug carriers with tertiary amine groups, we newly designed and synthesized poly{α-[4-(diethylamino)methyl-1,2,3-triazol]-caprolactone--caprolactone}--poly(2-methacryloyloxyethyl phosphorylcholine) (PDCL-PMPC), a biomimetic phosphorylcholine polymer with pH-ensitive groups. PDCL-PMPC self-assembles into small and uniform micelles as its counterpart poly(caprolactone)--poly(2-methacryloyloxyethyl phosphorylcholine) (PCL-PMPC) without pH-sensitive groups. The in vitro and in vivo properties of PDCL-PMPC and PCL-PMPC micelles are investigated in detail. PDCL-PMPC micelles display obvious pH sensitivity by micelle change and fast drug release at pH 5, but the insensitive micelles do not. The internalization of PDCL-PMPC micelles by tumor cells is stronger than that of PCL-PMPC micelles. However, in comparison with the insensitive micelles, the pH-sensitive micelles present much shorter blood circulation time in pharmacokinetics and demonstrate worse accumulation in the tumor site in vivo study. As a result, DOX loaded PCL-PMPC micelles demonstrate much better antitumor efficiency than pH-sensitive micelles. Furthermore, DOX loaded PCL-PMPC micelles show similar therapeutic efficacy to DOX·HCl but with considerably lower side effects.